ICD's are designed to detect atrial and/or ventricular fibrillation and, in response to the detection, to deliver high voltage shock therapy in order to terminate the fibrillation. FIG. 1 is a schematic showing a typical subcutaneous pectoral placement of an ICD 100 in a patient 102, wherein a hermetically sealed and biocompatible canister 104 of ICD 100 houses circuitry to enable detection and therapy delivery via one or more electrical leads 106, which are coupled to the circuitry and extend distally from canister 104, through the venous system 110 and into the heart 108 of patient 102, for example, the right ventricle (RV). Those skilled in the art understand that the one or more leads 106 include sensing and defibrillation electrodes, and, in most cases, pacing electrodes as well. The electrodes of lead(s) 106 are coupled to the ICD circuitry via one or more lead connectors that terminate elongate insulated conductors of the electrodes, at a proximal end of lead(s) 106; the one or more lead connectors are plugged into a connector module 105, which is mounted on canister 104, to make electrical contact with the contained ICD circuitry via hermetically sealed feedthroughs. Canister 104, for example, formed from a Titanium alloy, is typically employed as a high voltage electrode in conjunction with a high voltage electrode of lead(s) 106 to establish an effective shocking vector for cardiac defibrillation.
FIG. 2 is a simplified block diagram of a portion of the ICD circuitry, wherein a battery 202 provides operating power to a controller 204 and to a shocking circuit 206. Controller 204, which controls the delivery of energy through the electrodes of lead(s) 106, can be any type of control circuitry suitable for determining when, where and for what duration the energy may be delivered. In order to generate a voltage, for example, approximately 750 volts or more, which is necessary to deliver defibrillation shock energy, for example, at a level in the range of 5-40 Joules, shocking circuit 206 includes a capacitor element 211. A transformer assembly 210 of shocking circuit 206 typically comprises a flyback transformer coupled between battery 202 and capacitor element 211 for incremental charging of capacitor element 211. Once capacitor element 211 is charged and called upon by controller 204, a switch 212 of shocking circuit 206 connects capacitor element 211 for the routing of a high voltage pulse through to the appropriate electrodes of ICD 100.
In the past, a conventional type of transformer assembly 210 would be constructed from components that are physically separate from one another and from other electrical components of the ICD circuitry, for example, primary and secondary windings formed around a toroid-shaped magnetic core. Because these components of the conventional transformer assembly 210 take up a relatively large amount of space within canister 104, recent efforts to reduce an overall size of canister 104, for a more comfortable implant, have focused on reducing the size of flyback transformers that are employed for charging ICD capacitors. Commonly-assigned U.S. Pat. No. 7,167,074 describes the construction of planar flyback transformer assemblies, for physical integration of the transformer with other circuitry of an ICD, wherein primary and secondary windings are embedded between opposing sides of a printed circuit board (PCB) to which a planar magnetic core is mounted (i.e. E-shaped core with legs/feet extending through openings in the PCB such that the windings are disposed thereabout). Although the embodiments of planar flyback transformers that are described in the '074 Patent can reduce the amount of space taken up by a transformer assembly, such as assembly 210 within canister 104, there is still a need for improved configurations of planar flyback transformers that are particularly suited for charging capacitors of ICD's.